High energy propulsion method using aluminum and water



Unite This invention relates to compositions of materials which may react chemically together to release large amounts of heat energy. The energy released may be used for rocket propulsion, for generating thrust or power for other applications, or for heating materials or spaces to high temperatures. The mixtures may also be reacted for the purpose of producing either or all of the major components of the products of reaction, for producing these reaction products at high temperature, or for other unique purposes.

Specifically, this invention relates to compositions of aluminum and water, in approximately stoichiometric proportions, which may be combined and reacted in a variety of ways for a variety of purposes, and also relates to several unique methods of application particularly suited to practical exploitation of these compositions.

Mixtures of materials ordinarily used for propelling rockets, for heating the chambers of furnaces or kilns, for use as an explosive, for welding, or for otherwise generating heat energy at high temperatures, are comprised of a fuel, an oxidizer, and sometimes additional materials to modify the rate or character of energy release. The fuel and oxidizer themselves often are each comprised of a mixture of chemically different materials. Sometimes the fuel and oxidizer are kept separate, and are mixed together only at or immediately before the time of reaction; sometimes they are mixed together and stored as a mixture until use. Sometimes the fuel and oxidizer are chemically combined into one unstable compound.

The fuel is a material which releases a large amount of heat energy when combined with any of a small group of so-called oxidizing elements usually taken to consist of oxygen, fluorine, and chlorine. The oxidizer may be any of that small group of elements, or a material containing a high proportion of such elements, and which under suitable conditions will release the oxidizing elements to a fuel without in so doing absorbing more than a small part of the total energy released by the oxidation reaction.

Either or both the fuel and oxidizer may be a gas, a liquid, or a solid; or a mixture of phases; though gases are usually impractical in mobile self-contained applications because of the large vessels or heavy walls required for storage.

In practical applications the choice of fuel and oxidizer is governed by a balance of such considerations as the theoretical amount of energy available, the range of compositions, temperatures, and pressures under which the components will react controllably, the cost and availa bility of fuel and oxidizer, and the ease and safety with which reactants and reaction products may be handled, stored, transported or otherwise manipulated.

"For rocket propulsion it is necessary that there be a large amount of energy released in proportion to the total weight of fuel and oxidizer. The materials currently selected, in order to attain this characteristic, are all far from ideal in one or more other desirable characteristics.

The ideal fuel would not only have a high available energy potential, but it also would be available at low cost in large quantity, chemically stable at ordinary temperatures when in contact with air, water, and materials of construction, and strong yet formable and with a high melting point if to be used as a solid. Solid fuels would be better for many rocketry and other applications than States Patent gas or liquid fuels, except for the disadvantage that in current practice it is not generally possible to control or extinguish the burning, especially if a solid oxidizer is used.

The ideal oxidizer would be stable against dCCOlTlPOSI- tion at ordinary temperatures when in contact with air, water, or ordinary materials of construction, yet require a relatively low absorption of energy per unit of oxidizing element released. It would be available at low cost, in large quantity. A fluid oxidizer is best for use in a controllable reaction with a solid fuel, though for non-controllable reactions with a solid fuel a solid oxidizer may have advantages.

The ideal combination of fuel and oxidizer would release a large amount of energy, would be permanently stable when stored in the combined state at ordinary temperatures and would generate as products of reaction only materials which are non-toxic, non-corrosive, and readily removable from the reaction zone. For any high-temperature process, the reaction products should have low specific heats, and should not vaporize or should vaporize with small heats of vaporization; for rocketry they should also have, generally, the properties of a good propellant.

Aluminum, when reacted to its oxide, releases more energy per pound of oxide than any element except hydrogen, lithium, boron or beryllium, and about the same as magnesium or silicon. All of these elements other than aluminum, have disadvantages.

Hydrogen, though widely used, is difficult and dangerous to handle, and cannot be used as a solid. Lithium is expensive, ignites spontaneously in cold water, and reacts with air, and its oxide melts at such a low temperature that it is likely to be liquified during the reaction, thereafter to solidify and deposit in other parts of the engine. Beryllium is rare and expensive, and both it and some of its compounds are toxic. Boron oxide is a low-melting powerful flux which will cause rapid deterioration of many materials of construction. Magnesium is hazardous because of its combustibility in air. Silicon produces an oxide which is a viscous fluid with a tendency to deposit on parts of the engine.

Aluminum alone of the high-energy elements has all of the following characteristics: it is available in unlimited quantities at low cost, it is stable in air and water over a wide temperature range, it and its oxides are nontoxic, non-corrosive, and non-fluxing. It is a strong solid with relatively high melting temperature. It is easily formed into desired shapes, and its oxide has an extremely high melting temperature.

Of all the elements and known compounds, aluminum approaches most closely many of the characteristics of the ideal fuel. For this reason it has often been used as the fuel in thermochemical reactions for metallurgical applications, as a major or minor component of explosives and pyrotechnics, and as a minor additive to the fuel of rockets. It has not been used as the major component of a rocket fuel, or for a number of other possible fuel applications, because of the difficulty of controlling the energy release.

The solution of this problem is made easier by choice of the right kind of oxidizer.

In any application, an oxidizer based on oxygen is preferable, if suflicient energy can be developed from its use, because fluorine and chlorine and many of their compounds are toxic or corrosive and fluorine is expensive as well.

Except for liquid oxygen itself, the oxygen-based oxidizers tend to be chemically unstable, which can make them hazardous, especially while they are being blended with a solid fuel.

Water, with an oxygen content of 89% by weight, contains more oxygen than any oxidizer except hydrogen peroxide or pure oxygen. Water is not ordinarily thought of as a powerful oxidizer, and in fact with most fuels, little or no useful energy can be released by water because of the relatively large absorption of energy required to release its oxygen, and also because of the high specific heat and heat of vaporization of liquid water. But Water will react with aluminum to release a large amount of energy, provided the normal, thin, dense, protective coating of aluminum oxide is removed so that the water can contact the aluminum. Although water absorbs more energy in releasing its oxygen than do many of the other oxidizers, the net release of energy in the reaction of water with aluminum is usefully large. Furthermore, since aluminum oxide and hydrogen gas are the only reaction products, an extremely high product temperature is attainable.

Water, of course, is superior to most materials in cost, availability, ease of handling as either a liquid or solid, and chemical stability even when in prolonged contact with the aluminum fuel. Water is a good solvent or carrier for many modifiers which might be desired, such as hydrogen peroxide or other oxidizers, or other fuels, or chemicals to aid in dissolving the protective oxide coating that is normally present on the aluminum fuel. Water has the further advantage that when used in excess it can lower the reaction temperature, even to the extent of slowing or stopping the reaction. -It can also be used in a rocket to increase the mass of ejected propellant or to lower the temperature near structural parts of the engine.

To achieve maximum temperature in the products of reaction, the aluminum and water should be mixed in approximately stoichiometric proportions:

(solid) (liquid) (solid) (gas) or or (so.id) (liquid) This reaction will release about 1700 kilocalories per kilogram of product, which can raise the products to a very high temperature. The exact amount of surplus, useful, energy released will vary depending on the physical and chemical state of the reaction products, which depends in turn on the final temperature attained by these products. Therefore, the amount of energy and the temperature will depend on the configuration of the reaction vessel as well .as on the rates at which reactants are made available and heat and products are removed.

Variations in the proportions of aluminum and water will affect the amount and character of energy release. For rocket propulsion, the gaseous hydrogen emitted will generally be a most desirable propellant, but excess water in the exhaust may, in some circumstances provide more desirable thrust characteristics, or a more suitable temperature. Mixtures of aluminum and water are stable under ordinary conditions, because aluminum, in all forms in which it normally is prepared, is always covered by a very thin, dense, insoluble, protective, coating of aluminum oxide. In order to cause ignition, it is necessary to cause the oxidizing elements to penetrate this coating, and in order to sustain the oxidizing reaction it is necessary either to prevent the coating from reforming or to remove it as quickly as it does form. This may be done by heating the mixture above a critical temperature, or by using chemical means to make the oxide coating soluble or porous,

When aluminum and water are mixed in stoichiometric proportions they will coexist in the ratio of 2 atoms of aluminum to 3 molecules of water, which is very close to a one to one weight ratio which is also a volumetric ration of approximately 1.0 volume of aluminum to 2.7 volumes of water. It is easy to design a great many configurations by which the aluminum and water may be brought into contact in these proportions, with the water completely covering the surface of the aluminum, as will usually be desired.

This invention provides a novel composition of fuel and oxidizer which will perform many new and unique functions heretofore impossible. It is understood that a variety of conventional equipment will be useful with these compositions. Other new, unique designs of equipment may he invented to take full advantage of these compositions. It is not intended that the descriptions of specific applications or equipment included herein should limit the scope of the application of the compositions covered by this invention. The methods of application described in the claims herein, however, are intended to further demonstrate some of the unique characteristics of these compositions, as well as being in themselves, descriptions of new inventions. It is understood that various changes and additions may be made in formulating, compounding, and preparing the compositions of this invention and that the proportionate amount of ingredients may be varied over a relatively wide range,

depending upon the particular use to which the compo sition is to be put. Such changes and additions are contemplated to come within the spirit and scope of this invention, which are more particularly set forth in the following claims.

I claim:

1. The method of creating force in a reaction motor process by ejecting the product of chemical reaction consisting of chemically reacting solid aluminum as a fuel with water as an oxidizer wherein the reactants are present in the ratio of two aluminum atoms to three molecules of water and wherein about 1700 kilocalories per kilogram of product are released.

2. The method of claim 1 wherein hydroxyl ions are added to the water.

3. The method of claim 1 wherein the aluminum is in configurations consisting of porous and perforated aluminum blocks containing stoichiometric amounts of water.

4. The method of claim 1 wherein the aluminum is in the form of perforated blocks with less than the stoichiometric amount of water and wherein additional water is controllably injected through the block to the reaction surface in order to modify the reaction rate.

References Cited UNITED STATES PATENTS 3,191,535 6/1965 Mulloy 149-17 XR 3,203,172 8/1965 Sutherland 60--219 XR 1,506,322 8/1924 ONeill 149-37 X 1,506,323 8/ 1924 'ONeill 149-37 X 1,828,784- 10/1931 Perrin 60-39.59 2,937,824 5/ 1960 Krumbholz et a1. 149-37 X 3,019,687 2/1962 Gongwer 149-37 X 3,158,994 1/ 1964 Hodgson 60-220 3,182,554 5/1965 Barakauskas 89-1.81

BENJAMIN R. PA'DGE'I'I, Primary Examiner. 

1. THE METHOD OF CREATING FORCE IN A REACTION MOTOR PROCESS BY EJECTING THE PRODUCT OF CHEMICAL REACTION CONSISTING OF CHEMICALLY REACTING SOLID ALUMINUM AS A FUEL WITH WATER AS AN OXIDIZER WHEREIN THE REACTANTS ARE PRESENT IN THE RATIO OF TWO ALUMINUM ATOMS TO THREE MOLECULES OF WATER AND WHERIN ABOUT 1700 KILOCALORIES PER KILOGRAM OF PRODUCT ARE RELEASED. 